1. Field of the Invention
The present invention relates to a plane light source device, and more particularly to a backlight module and a light guide plate used in the backlight module.
2. Description of the Related Art
With the development of flat panel display technique, flat panel displays (FPDs) that have advantages of light in weight, small in size and low power consumption are becoming more and more popular. Typically, the flat panel displays include liquid crystal displays (LCDs), plasma panel displays (PDPs), organic light emitting diode displays (OLED displays) and electrophoretic displays (EPDs). Among the flat panel displays, the liquid crystal displays are most widely used.
The liquid crystal display includes a liquid crystal display panel and a backlight module. The backlight module is used to provide a plane light source to the liquid crystal display panel. Generally, the backlight module may be classified into a direct type backlight module and a sidelight type backlight module based on a transmission mode of light.
FIG. 1A is a schematic view of a conventional sidelight type backlight module. FIG. 1B is a schematic side view showing a light guide plate of FIG. 1A. Referring to FIGS. 1A and 1B, the conventional backlight module 100 includes a light source 110, a light guide plate 120, a reflective sheet 130 and an optical sheet 140. The light guide plate 120 includes a light incident surface 122, a light emitting surface 124 and a bottom surface 126. The light emitting surface 124 is opposite to the bottom surface 126. The light incident surface 122 is connected between the light emitting surface 124 and the bottom surface 126. The light source 110 is disposed adjacent to the light incident surface 122. The reflective sheet 130 is disposed under the bottom surface 126. The optical sheet 140 is disposed above the light emitting surface 124. In addition, a plurality of sandblasted structures 125 is formed on the light emitting surface 124, and a plurality of V-shaped light guide units 127 is formed on the bottom surface 126.
When a portion of light rays (such as light ray 112) provided by the light source 110 transmits to a surface 127a of the V-shaped light guide unit 127, the portion of light rays (such as light ray 112) would be totally reflected, and a light emitting angle of the portion of light rays (such as light ray 112) is relatively small when emitting from the light emitting surface 124. In the conventional backlight module 100, the portion of light rays (such as light ray 112) which is totally reflected can be utilized. In addition, the light rays (such as light ray 114) transmitting to the sandblasted structures 125 would be diffused. However, a portion of the diffused light rays (such as light ray 115) could not emit from the light emitting surface 124. Accordingly, light emitting efficiency of the conventional light guide plate 120 would be reduced, and light utilization efficiency of the conventional backlight module 100 would be decreased. In addition, the sandblasted structures 125 would make it difficult to control the light emitting angle of the light rays. Consequently, brightness and uniformity of the light rays emitting from the light guide plate 120 are not easily adjusted, and the light emitting surface 124 of the light guide plate 120 may appear some bright areas (or bright strips) and dark areas (or dark strips).